Question

No heat from heater core. 1995 Chevy 2500 truck.

1995 Chevy 2500 truck, no heat coming from heater core, replaced water pump, heater core. Thermostat seems like the water is not flowing. Have heater core laying open and it is not getting hot. Before I changed the heater core, it would get hot, till you turn on the fan, it would cool off one side of the hose.

update on no heat , the one line that goes from heater core to the intake manifold on the back of the motor , it is the fitting that you press in the heater hose into , upon removal, it was plugged soild, replaced with new fitting & lots of heat now, hope this help others.

I went to answer your post, and advise that you would need to inspect for that restriction, it is very common for vehicles that generally have not had proper maintenance performed thru the years. I would also recommend using a BG coolant flush additive and flush the system. With that much electrolysis build up, you may even have a partially restricted radiator. This can be inspected visually, and by using an Infra Red Thermometer. After the vehicle is at operating temperature, use the IR thermometer to check the temperature across the entire surface of the radiator. you may find variations of temp, which would indicate restriction.